HMGB1 and primary progressive multiple sclerosis: When we segregated patients on the basis of clinical forms (Figure 1B), HMGB1 expression levels were higher in PBMC from patients with relapse-onset MS, and differences were statistically significant for RRMS patients when compared both with PPMS patients and controls (P = 4 × 10−5 and P = 0.005, respectively), and also for SPMS patients when compared with PPMS patients (P = 0.001).